1. Field of the Invention
The present invention relates to a tank valve apparatus, and particularly to a tank valve apparatus, for a tanker truck or the like.
2. Description of the Prior Art
Tank valve apparatus for fuel tanker trucks typically provides adequate internal venting of the tank at all times, as required by Federal and many state regulations. In addition, such apparatus operates to provide much more rapid venting in the event that excessive or explosive pressures develop in the tank. Such venting is particularly important during rapid filling of the tank. Equally importantly, such valve apparatus operates to admit air during rapid discharge of fuel to prevent collapse of the tank. However, the prior art mechanisms available to accomplish the foregoing are often complex in construction and operation, and consequently are expensive, difficult to operate and characterized by high maintenance costs and sometimes short service life. Some are even unreliable by reason of their complexity or faulty design.
An unfortunate consequence of the high speed transport of fuel and similar product in tanker trucks operating on crowded highways is the increasing incidence of accidents in which the tanker truck rolls over. Prior valve apparatus is ineffective in such instances to seal the tank against fuel spillage and the sometimes catastrophic release of large quantities of fuel.
It has been found that on tank rollover there is a very sudden liquid surge which in as little as two milliseconds develops internal pressures in the order of fifty pounds per square inch, which persists for approximately fifty milliseconds. No adequate means is available for reducing the sudden effect of such a liquid surge, which has resulted in blowing the manhole or dome cover assembly completely off the tank, and thereby releasing large quantities of fuel through the large opening that results.
In those instances where the dome assembly has held in such rollovers, significant quantities of fuel are sprayed out through the vent valve system, creating a highly inflammable fuel fog in the vicinity. Prior art vent systems are either not capable of closing at all under such conditions, or they react too slowly to the rapidly rising tank pressures to close before a great deal of fuel is sprayed out.